Transparent dental care composition

ABSTRACT

A dental-care composition having improved shelf life in respect of rheology and abrasiveness, which, as a novel feature, contains, as a cleansing agent, a bifunctional (thickening and abrasive) precipitated silica characterized by the following physico-chemical properties: 
     
         ______________________________________                                    
 
    
                      Pendulum                                                 
                 roller                                                   
                 mill     Jet mill                                        
______________________________________                                    
BET surface area                                                          
               m 2  /g                                                 
                       15-110     15-110                                  
Tamped density g/1     150-750    90-650                                  
Secondary particle size                                                   
                       FIG. 1     FIG. 2                                  
distribution according to                                                 
Coulter Counter                                                           
&#34;ALPINE&#34; screen                                                           
               % by    &lt;1.5       &lt;0.1                                    
retainings &gt;63 μm                                                      
               weight                                                     
Cu abrasion in 10%                                                        
               mg      5-30       5-30                                    
strength glycerol disper-                                                 
sion                                                                      
Lightness value A                                                         
               %       86-96      90-96                                   
Viscosity in a 30%     30,000-60,000                                      
                                  30,000-60,000                           
strength dispersion in a                                                  
1:1 glycerol/water                                                        
mixture, Brookfield RTV,                                                  
Sp5                                                                       
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     The dental-care composition may additionally contain 0.5-5% by weight of polyethylene glycol or 2-14% by weight of a precipitated silica which in 15% strength dispersion in a glycerol/water mixture has a viscosity of not less than 30,000 mPa.s. Pyrogenic silica can also be employed successfully to regulate the viscosity of the product.

REFERENCE TO A RELATED APPLICATIONS

This application is a division of our copending application Ser. No.773,973 filed Sept. 9, 1985, now U.S. Pat. No. 4,664,907, which in turnis a continuation of copending application Ser. No. 641,812 filed Aug.17, 1984, abandoned, which in turn is a continuation of copendingapplication Ser. No. 510,452 filed July 1, 1983, abandoned, which inturn is a continuation of copending application Ser. No. 364,035 filedMar. 31, 1982, abandoned, and all relied on.

It is known that amorphous synthetic silicas may be used as cleansingagents in toothpastes. Silicas, used as cleansing agents, have the vitaladvantage over the previously used calcium phosphates and chalks thatthey do not react with the fluoride ions frequently employed in the formof tin(II) fluoride and sodium fluoride as anti-caries agents, and thusdo not block the effect of these additives.

Accordingly, there is a need to replace the cleansing agents based oncalcium phosphates and chalks by an inert substance.

A first vital successful step in this direction was the introduction ofamorphous high porous silica xerogels (U.S. Pat. No. 3,538,230), thecombination of which with thickening aerogels, for example Syloid 244®,finally allowed the commercial breakthrough of the use of silica gels intoothpastes. However, it must be pointed out that use had been made muchearlier of the viscosity-regulating effect of certain silicas, forexample pyrogenic and precipitated silicas having a high degree ofstructure (German Pat. No. 1,667,875 corresponding to U.S. Pat. No.3,705,940 and British Pat. No. 1,241,877). In subsequent development,the combination of cleansing agents based on silica xerogels withpyrogenic silicas (German Published Application DAS No. 2,033,678corresponding to U.S. Pat. No. 3,689,637 and British Pat. No. 1,298,130)and with thickening precipitated silicas having a medium to high degreeof structure (British Pat. No. 1,433,743, German Published ApplicationDAS No. 2,610,207 and U.S. Pat. No. 4,132,806) was, logically, alsopursued.

The next step with regard to the production of improved novel cleansingagents was the development of a specific aluminum silicate produced byprecipitation, and the combination of this silicate with a thickeningpyrogenic silica or with a thickening precipitated silica of medium tohigh degree of structure is described in German Pat. No. 2,154,376corresponding to British Pat. No. 1,400,793 and German PublishedApplication DAS No. 2,206,285 corresponding to British Pat. No.1,372,663.

Subsequent development next led to cleansing agents based onprecipitated silicas which produced no significant thickening action buthad markedly lower abrasiveness than the calcium phosphate cleansingagents. Where these novel SiO₂ -based precipitated silicas are used, therheology of the toothpastes is not regulated by means of thickeningprecipitated silicas, but by addition of special binders such as seaweedcolloids or synthetic cellulose derivatives (carragheen and sodiumcarboxymethylcellulose) and by means of vegetable gums (German Laid-OpenApplication DOS No. 2,344,316; U.S. Pat. No. 4,105,757; German Laid-OpenApplication DOS No. 2,344,805; U.S. Pat. Nos. 4,122,160 and 4,144,321,and German Laid-Open Application DOS No. 2,522,486 corresponding to U.S.Pat. Nos. 4,067,746 and 4,191,742).

Nowadays, a modern cleansing agent based on silicas and intended for usein toothpastes has to provide the following effects:

reduced abrasiveness, in the sense of medium polishing activity (Cuabrasion in the finished toothpaste, between 8 and 14 mg), in order toprotect the dental enamel,

at filler contents in the range of 15-25% by weight, based on the amountof one and the same bifunctional cleansing agent (producing bothabrasion and thickening), the viscosity, under conditions which give theabove Cu abrasion range, should be between 2,500 and 4,500 mPa.s(determined by the Rotovisko-PK method),

the ribbon of toothpaste leaving the tube should be smooth, glossy andfree from specks and

the dental-care composition containing the cleansing agent should haveimproved shelf life, in the sense of exhibiting constant abrasivenessand degree of thickening (no after-thickening) for a period of at leastone year.

It is an object of the invention to conform to the above requirements ofa dental-care composition by choice and use of a suitable cleansingagent.

We have found that this object is achieved as follows:

We resort to a process for the preparation of precipitated silicaswhich, depending on the manner in which they are milled, givesprecipitated silicas having the following physico-chemicalcharacteristics:

    ______________________________________                                                           Pendulum                                                                      roller                                                                        mill    Jet mill                                           ______________________________________                                        BET surface area determined                                                                    m.sup.2 /g                                                                             15-110   15-110                                     according to DIN 66,131                                                       Tamped density determined                                                                      g/l     150-750   90-650                                     according to DIN 53,194                                                       Cu abrasion in 10% strength                                                                    mg       5-30     5-30                                       glycerol dispersion                                                           Viscosity of a 30% strength                                                                    mPa · s                                                                      30,000 to 60,000                                     dispersion in a 1:1 glycerol/                                                 water mixture (Brookfield                                                     RTV, Sp5)                                                                     Lightness value A                                                                              %       86-96     90-96                                      according to DIN 55,921                                                       Secondary particle size  according according                                  distribution curve according                                                                           to FIG. 1 to FIG. 2                                  to Coulter counter                                                            "ALPINE" screen retainings                                                                     % by    <1.5      <0.1                                       >63 μm        weight                                                       ______________________________________                                    

Such precipitated silicas are very particularly suitable for use in thenovel dental-care compositions which are intended to exhibit the patternof properties referred to above.

The process for the preparation of precipitated silicas having the abovepattern of properties is characterized in that an original precipitatedsilica suspension, which is prepared by precipitating the silica in aninitial charge of alkali metal silicate solution, having a concentrationof about 5-25 g of SiO₂ per liter of solution, by means of an acid andalkali metal silicate solution of particular concentrations, atparticular feed rates, while maintaining a precipitation temperature inthe reaction medium between 80° and 90° C., the precipitation beingcarried out under such conditions that the viscosity of the reactionmedium is kept, for at least 30% of the total precipitation time, at auniform low value while the pH is kept between 10 and 12, and theaddition of the reactants only being terminated when the viscosity,after passing through a maximum, has dropped to a value which is lessthan 100% above the initial value, is diluted with hot water to aprecipitated silica content of 10-30 g/l and a sodium sulfate content of6-20 g/l, and heated to 85°-95° C., the pH is brought to 7-9 withsulfuric acid and, while keeping this pH value constant, alkali metalsilicate solution, sulfuric acid and hot water are added simultaneouslyover a precipitation period of 30-180 minutes so as to give a finalconcentration of precipitated silica of 40-80 g/l, the suspension isacidified with concentrated sulfuric acid to a pH below 7, and theprecipitated silica is separated from the suspension by means of afilter press, washed out, dried and milled by means of a pendulum rollermill or jet mill.

In a preferred embodiment, it is possible to use an originalprecipitated silica suspension which has been subjected to intensiveshearing during its phase of preparation according to German PublishedApplication DAS No. 1,467,019. This is of advantage wheneverparticularly high Cu abrasion values are to be achieved. In a particularembodiment of the invention, shearing can be effected according toGerman Pat. No. 1,767,332.

The present invention provides a dental-care composition having improvedshelf life in respect of rheology and abrasiveness, which contains, as athickener and abrasive, a precipitated silica characterized by thefollowing physico-chemical properties:

    ______________________________________                                        BET surface area determined                                                                      m.sup.2 /g                                                                            15-110                                             according to DIN 66,131                                                       Tamped density     g/l     90-650                                             Secondary particle size                                                                          according to FIG. 2                                        distribution curve accord-                                                    ing to Coulter counter                                                        "ALPINE" screen retainings                                                                       % by    <0.1                                               >63 μm          weight                                                     Cu abrasion in 10% strength                                                                      mg      5-30                                               glycerol dispersion                                                           Viscosity of a 30% strength                                                                      mPa · s                                                                      30,000-60,000                                      dispersion in a 1:1 water/                                                    glycerol mixture (Brookfield                                                  RTV Sp 5)                                                                     Lightness value A  %       90-96                                              according to DIN 55,921                                                       ______________________________________                                    

The dental-care composition according to the invention exhibits thefollowing advantageous properties:

it possesses mild abrasiveness, in the sense of medium polishing actionon the surface of the teeth, without damaging the dental enamel,

if 15-25% by weight of cleansing agent, based on a single silica, areused, mild abrasion (8-14 mg Cu abrasion) coupled with optimum rheologyof the paste (viscosity between 2,500 and 4,500 mPa.s determined by theRotovisko method) can be achieved,

the ribbon of toothpaste is smooth, speck-free and glossy and

the toothpaste exhibits improved shelf life in respect of constancy ofabrasiveness and thickening (without after-thickening).

The invention further provides a dental-care composition with improvedshelf life in respect of rheology and abrasiveness, which contains, asthe abrasive, a precipitated silica characterized by the followingphysicochemical properties:

    ______________________________________                                        BET surface area determined                                                                       m.sup.2 /g                                                                             15-110                                           according to DIN 66,131                                                       Tamped density      g/l     150-750                                           Secondary particle size dis-                                                  tribution according to FIG. 1                                                 "ALPINE" screen retainings                                                                        % by    <1.5                                              >63 μm           weight                                                    Cu abrasion in 10% strength                                                                       mg       5-30                                             glycerol dispersion                                                           Viscosity of a 30% strength                                                                       mPa · s                                                                      30,000-60,000                                     dispersion in a 1:1 glycerol/                                                 water mixture (Brookfield                                                     RTV Sp5)                                                                      Lightness value A   %       86-96                                             according to DIN 55,921                                                       ______________________________________                                    

The dental-care composition according to the invention can have a totalprecipitated silica content of 17 to 25% by weight, preferably of 17 to22% by weight. If the abrasive silica is used as the sole silicacomponent, its concentration is 20 to 25% by weight, preferably 20 to22% by weight. If mixtures of abrasive precipitated silica andthickening precipitated silica are employed, the followingconcentrations result: 15 to 20% by weight of abrasive precipitatedsilica 2 to 14% by weight, preferably 2 to 10% by weight, of thickeningsilica.

This novel dental-care composition has the following advantageousproperties:

it possesses mild abrasiveness, in the sense of medium polishing actionon the surface of the teeth, without damaging the dental enamel,

improved shelf life in respect of constant abrasiveness and thickening(without after-thickening) for a period of at least one year.

In a particular embodiment, 0.5-5% by weight of polyethylene glycolhaving a molecular weight in the range from 400 to 2,000 may be added,as a thickener, to the recipe of the dental-care composition. Thismeasure has the effect of either reducing the amount of cleansing agentneeded for a given final viscosity of the dental-care composition or ofproducing, at constant cleansing agent concentration, a higher viscosityof the toothpaste (for example, a different viscosity may be neededdepending on whether the toothpaste is packed in a tube or a dispenser).

In a further embodiment, there may also be added to the toothpasterecipe 2-14% by weight, preferably 2-10% by weight, of a precipitatedsilica, available, for example, under the trademarks FK 320 DS, Sipernat22 S®, FK 300 DS, ZeoSil 200 or Sident 11®, which in 15% strengthdispersion in a 1:1 glycerol/water mixture has a viscosity of not lessthan 30,000 mPa.s., or 0.5-4% by weight, preferably 2-4% by weight, of apyrogenic silica which is available, for example, under the tradenamesAerosil 200®, Cabosil M5®, Aerosil 200 V® or HDK N 20 E, together withcleansing agents, as thickener. In this way, the polishing action of thedental-care composition can be increased by using a silica cleansingagent which has a marked abrasive action but is in general a lesseffective thickener, if, at the same time, the reduction in thickeningaction is compensated by addition of precipitated silicas or pyrogenicsilicas having an appropriate thickening action. This situation applies,for example, when formulating a smoker's toothpaste.

By combination of the SiO₂ cleansing agents, used in the noveldental-care composition, with thickening additives such as polyethyleneglycol or pyrogenic or precipitated silica, the dental cosmetician isprovided with means which allow him a substantial extension of theusefulness of the noveal dental-care compositions. At the same time itis to be borne in mind that these embodiments also have substantiallyimproved properties in respect of shelf life of the composition.

Of course, the dental-care compositions according to the invention canbe prepared either in a transparent or in an opaque form.

Principal constituents of transparent toothpastes:

water, glycerol and cleansing agent, the latter being silicon dioxide(silica).

Subsidiary constituents:

binders, eg. carboxymethylcellulose, preservatives (eg. sodiumbenzoate), sweetener (eg. saccharin), aromatic oils, foaming agents (eg.sulfonates), active ingredients, eg. fluorides, and dyes.

Principal constituents of opaque pastes:

cleansing agents, water and sorbitol.

In opaque pastes, the cleansing agents may also include chalks, aluminumhydroxides and calcium phosphates in addition to silicas and amorphoussilicates (sodium aluminosilicates).

Subsidiary constituents:

binders (eg. carboxymethylcellulose), preservatives (eg. Na benzoate),sweetener (eg. saccharin), opacifiers (eg. TiO₂), active ingredients(eg. fluorides), foaming agents (eg. sulfonates) and, if desired, dyes.

The examples which follow illustrate and describe the novel dental-carecompositions in comparison with prior art compositions.

The precipitated silicas, pyrogenic silicas and silica xerogels used toprepare the dental-care compositions are summarized in Survey Table No.1 on page 12, together with those of their physico-chemical data whichare considered relevant to their use in toothpastes. In the examplessection, the letters A-I are employed in connection with the recipe andthe description of the results. The letters A-D designate the abrasivesilicas using in the dental-care composition according to the invention.In addition to the silica-containing toothpaste fillers listed in thetable, the following fillers are used for comparative experiments: chalk(CaCO₃), produced by Schafer, Diez/Lahn, West Germany. Dicalciumphosphate dihydrate, produced by Benckiser-Knapsack, West Germany.Titanium dioxide RN 56, produced by Kronos AG, West Germany.

All other toothpaste raw materials contained in the recipes given arelisted in alphabetical order, together with information on suppliers, inSurvey Table No. 2.

To demonstrate the technical effects, and for comparativeinvestigations, essentially four basic recipes are used in the examplessection, namely:

An opaque sorbitol paste which contains 40% by weight of sorbitol as themain constituent.

A transparent glycerol paste which contains 60% by weight of glycerol asthe main constituent.

A chalk paste containing glycerol.

A phosphate paste containing sorbitol and glycerol.

The exact composition of the pastes investigated is in each case givenin detail in the corresponding example sections. As a rule, an increasein the content of cleansing agent is compensated by a decrease in thewater content.

To produce the pastes, the components are compounded in a RETSCH mill,homogenized three times on a triple-roll mill and then deaerated in adesiccator using a vacuum pump.

                                      TABLE No. 1                                 __________________________________________________________________________    Precipitated silicas, pyrogenic silicas and silica xerogels, the use of       which in                                                                      dental-care compositions is described in the examples.                                                      Com-  Com-  Commercial                                                                           Commercial                                                                           Commercial                                          mercial                                                                             mercial                                                                             precipi-                                                                             pyrogenic                                                                            precipi-                                            SiO.sub.2                                                                           SiO.sub.2                                                                           tated  silica,                                                                              tated                 Physico-chemical                                                                        Abrasive                                                                           Abrasive                                                                           Abrasive                                                                           Abrasive                                                                           xerogel,                                                                            xerogel,                                                                            silica Aerosil                                                                              silica                characteristics                                                                         silica                                                                             silica                                                                             silica                                                                             silica                                                                             Syloid ALi                                                                          Syloid 63                                                                           FK 320DS                                                                             200 V  FK 300 DS             Type:     A    B    C    D    E     F     G      H      I                     __________________________________________________________________________    BET surface area,                                                                       103  101  70   51   633   719   170    200    300                   m.sup.2 /g                                                                    Secondary particle                                                                      FIG. 1                                                                             FIG. 2                                                                             FIG. 2                                                                             FIG. 2                                                                             FIG. 3                                                                              FIG. 4                                                                              FIG. 2 --     FIG. 2                size distribution,                                                            according to                                                                  Coulter Counter                                                               "ALPINE" screen                                                                          1.4  0.1  0.1  0.1 <0.1  <0.1  --     --     --                    retainings                                                                    >63 μm (% by                                                               weight)                                                                       Cu abrasion* (mg)                                                                        14   8   12   17   7-8   11-12 <1 mg  < 1 mg <1 mg                 Viscosity** (mPa.s)                                                                     36,000**                                                                           --   38,400**                                                                           33,500**                                                                           not   not   52,200***                                                                            --     54,000***                                           measurable,                                                                         measurable,                                                             too mobile                                                                          too mobile                                Lightness 94.4 96.8 95.7 94.6 --    94.1  --     --     --                    value A (%)                                                                   __________________________________________________________________________     *in 10% strength glycerol dispersion                                          **in 30% dispersion in a 1:1 glycerol/water mixture                           ***in 15% strength dispersion in a 1:1 glycerol/water mixture            

                  TABLE No. 2                                                     ______________________________________                                        Toothpaste raw materials and source of supply (excepting fillers)                                          Supplier                                         Raw material                                                                              Chemical name    company                                          ______________________________________                                        aromatic oil                                                                              peppermint oil,  Haarmann and                                                 oil of wintergreen                                                                             Reimer,                                                                       Dragoco                                          Dehydazol A 400 P                                                                         carboxymethylcellulose                                                                         Henkel                                           0.5% strength dye                                                                         foodstuff dyes   Siegle-Farben                                    solution                                                                      Glycerol    glycerol, German Merck                                                        Pharmacopeia 7                                                    Polyethylene glycol                                                                       polyethylene glycol                                                                            Merck                                            400                                                                           Polyethylene glycol                                                                       polyethylene glycol                                                                            Merck                                            1500                                                                          liquid paraffin                                                                           paraffin         Merck                                            saccharin   benzoic acid sulfimide                                                                         Bayer                                            sodium saccharin                                                                          sodium salt of   Bayer                                                        benzoic acid sulfimide                                            Solbrol M   methyl p-hydroxy-                                                                              Bayer                                                        benzoate                                                          Solbrol M--Na                                                                             sodium salt of methyl                                                                          Bayer                                                        p-hydroxybenzoate                                                 sorbitol    sorbitol         Maizena                                                      Karion F (70% strength                                                                         Merck                                                        aqueous sugar solution)                                           Texapon K 12                                                                              sodium laurylsulfonate                                                                         Henkel                                           ______________________________________                                    

Description of test methods and methods of measurement:

Determination of Cu abrasion in 10% strength glycerol dispersion

(a) Preparation of the glycerol dispersion

153 g of anhydrous glycerol (German Pharmacopeia 7; density=1.26 g/ml)are weighed into a 250 ml polyethylene beaker. 17 g of cleansing agentare carefully mixed into it by means of a spatula. The mixture is thenhomogenized with a paddle stirrer (diameter 5.2 cm) for 12 minutes at1,500 rpm.

(b) Method of measurement of abrasion

The abrasion is measured in an abrasion tester disclosed in thefollowing publications: (1) Pfrengle: Fette, Seifen, Anstrichmittel, 63(5) (1961), pages 445 to 451 "Abrasion und Reinigungskraft vonPutzkorpern in Zahnpasten" ("Abrasion and Cleansing Power of PolishingAgents in Toothpastes") (2) A. RENG and F. DANY, Parfumerie und Kosmetik59 (2) (1978), pages 37 to 45; "Anwendungstechnische Prufung vonZahnpasten" ("Performance Testing of Toothpastes"). For this purpose,the 6 troughs of the test apparatus were each covered with 20 ml of thehomogeneous dispersion. The abrasion produced by six plane-ground nylonbrushes on six plane-ground Cu sheets (electrolytic copper) in fivehours as a result of 50,000 reciprocating strokes is determined bydifferential weighing. In calculating the abrasiveness, the means of thevalues obtained are taken. The abrasion (abrasiveness) is quoted in mgof Cu.

Determination of Cu abrasion of opaque and transparent toothpastes

(a) Preparation of the toothpastes

See above description

(b) Method of measurement of abrasion

1. Principle

An important piece of information concerning the quality of thetoothpaste is the abrasiveness, which as a rule is determined by the RDAmethod and by the copper abrasion method. The values obtained giveimportant information on the cleansing action and abrasive action on thedental enamel and the neck of the tooth. To carry out the test, asuspension is prepared from the toothpaste and glycerol, and theabrasiveness of this mixture is determined with the abrasion tester.

2. Apparatus and reagents

Triple-roll mill (Optimat 1)

Abrasion tester

Analytical balance

Oven

Glycerol, anhydrous, German Pharmacopeia 7 (density=1.26 g/ml),

Toothpastes

3. Method

3.1 Preparation of the paste suspension

75 g of glycerol are stirred into 100 g of the toothpaste, in aporcelain dish, by means of a spatula, and the mixture is thenhomogenized 4 times on a triple-roll mill. The paste suspension obtainedis used for abrasion testing.

3.2 Measurement of abrasion

The determination is carried out in the abrasion tester. Six cleaned,plane-ground, accurately weighed electrolytic copper sheets are placedin the six troughs of the test apparatus. 20 ml of the homogeneousdispersion are then introduced into each. Plane-ground nylon brushes areplaced on the Cu sheets. The test is carried out with 50,000 doublestrokes (requiring about 5 hours). After completion of thedetermination, the copper sheets are rinsed first with water and thenwith acetone and are dried in a desiccator. The completely dry Cu sheetsare accurately weighed and the weight difference is quoted as theabrasiveness, in mg of Cu. In the evaluation, any outliers are ignored,and the mean of the remaining values is taken.

4. Evaluation

The abrasiveness is quoted in mg of Cu.

Weight of Cu sheet before determination minus weight of Cu sheet afterdetermination=loss of electrolytic copper in mg=abrasiveness. Test ofrheological activity of abrasive silicas in a 30% strength dispersion ina 1:1 glycerol/water mixture

    ______________________________________                                        1. Sample mixes                                                                          60 g    of silica                                                             70 g    of anhydrous glycerol, German                                                 Pharmacopeia 7, density 1.26 g/ml                                     70 g    of distilled water                                                    200 g   = 30% strength silica dispersion                           ______________________________________                                    

2. Method

The abrasive silicas are stirred manually for 1 minute, using a glassrod, into the glycerol/water mixture in a 400 ml beaker (squat form),and the mixture is left to stand for 24 hours, after which the viscosityis measured.

3. Measurement

The viscosity is measured in the same beaker, using the Brookfield RVTviscometer, spindle 5, at various speeds of revolution.

4. Calculation

Scale reading×factor=viscosity in mPa.s Test of rheological activity ofthickening silicas in a 15% strength dispersion in a 1:1 glycerol/watermixture

    ______________________________________                                        1. Sample mix                                                                            30 g    of silica                                                             85 g    of anhydrous glycerol, German                                                 Pharmacopeia 7, density 1.26 g/ml                                     85 g    of distilled H.sub.2 O                                                200 g   = 15% strength silica dispersion                           ______________________________________                                    

2. Method

The thickening silica is stirred manually for 1 minute, using a glassrod, into the glycerol/water mixture in a 400 ml beaker (squat form),and the mixture is left to stand for 24 hours, after which the viscositywas measured.

3. Measurement

The viscosity is measured in the same beaker, using the Brookfield RVTviscometer, spindle 5, at various speeds of revolution.

4. Calculation

Scale reading×factor=viscosity in mPa.s.

Determination of viscosity of toothpastes:

(a) Preparation of the toothpastes

See above description

(b) Method of measurement of viscosity

Testing the toothpaste viscosity on a Rotoviscometer, plate and conesystem

1. Apparatus

Rotovisko from Haake, Karlsruhe, West Germany, with thermostat,measuring head 50, plate-and-cone No. 8012 and 1224.

2. Method

The toothpaste is first brought to 20°-22° C. and a small amount is thenapplied with the end of a spatula to the plate. The measurement iscarried out at speed level 27. After 30 seconds, the scale value is readoff the indicator, since after this time an approximately constant valuehas been reached.

3. Evaluation

From the speed, pointer reading and calibration constant of theplate-and-cone system used, the viscosity of the paste is found from theequation

    V=K·S·U[mPa·s]

where

V=viscosity in mPa·s

U=speed level of the Rotovisko

S=scale reading

K=calibration constant of the cone used

Determination of the pH of toothpastes

(a) Preparation of the toothpastes

See above description

(b) Method of pH measurement

The pH of toothpastes is extremely important since it can greatly affectthe stability of a paste. Extremely alkaline and extremely acid pastesare as a rule undesirable, since they may cause bulging and corrosion ofthe aluminum tubes. Moreover, in the case of medicated toothpastes, theactive ingredient may be chemically attacked and decomposed. Pasteshaving a neutral pH are therefore preferred.

1. Apparatus

Laboratory pH-meter type 26 from Knick, with glass electrode.

2. Method

The glass electrode is dipped into the toothpaste and after about 3minutes the pH is read directly from the indicator.

Visual methods of assessment of dental-care compositions

(a) Assessment of the ribbon stability of a toothpaste

1. Method

The toothpaste is packed in an aluminum tube and a ribbon about 5 cmlong is then squeezed out onto a glass plate.

2. Assessment

The stability of the ribbon is assessed after 5 minutes. If the pastehas inadequate consistency, the ribbon is seen to have spread. Dependingon the width of the ribbon being assessed, the stability is rated 1-4.

(b) Assessment of the transparency of a transparent toothpaste

1. Method

(a) the paste is squeezed out between 2 glass plates or

(b) the paste is applied to a white sheet with black lines.

2. Assessment

re (a) The transparency of the paste may be judged very easily, sinceinadequate quality immediately manifests itself by clouding. Dependingon the degree of clouding, the transparency is rated 1-4.

re (b) If the paste has good transparency, the black line is veryclearly discernible through the ribbon of toothpaste. If thetransparency is less good, the line is more or less blurred. Thetransparency is rated 1-4.

(c) Assessment of the separation of toothpastes

1. Method

The paste is stored in aluminum tubes for 3 months at 45° C. andthereafter a ribbon about 5 cm long is pressed onto blotting paper.

2. Assessment

If the toothpaste has a tendency to separate, a film of moistureextending from the ribbon is readily visible in the blotting paper.Depending on the width of this film, the separation is rated 1-4.

Notes

The method described should be used as a rule, since in a few cases theseparation is so pronounced that a layer of liquid even forms at thetube nozzle.

1ST SERIES OF EXAMPLES

This series of examples is intended to demonstrate that the noveldental-care composition containing the cleansing agents specifiedtherein, which fulfils the double function of thickening andabrasiveness, meets today's market requirements in respect ofabrasiveness and consistency of opaque toothpastes, without otheradditives. Commercial cleansing agents based on silica gels do notexhibit these properties, as demonstrated by the comparative experimentsin the 1st series of examples.

The composition of the investigated opaque pastes is described in moredetail in Table No. 3 (recipes 1-12).

Table No. 4 shows the results (pH, Cu abrasion, viscosity, ribbonstability and separation) of the measurements carried out on recipes1-12. It follows from the results that:

Recipes No. 3 and No. 6, according to the invention, containing 25% byweight of cleansing agent B and C respectively, give toothpastes withstable ribbons and with an abrasiveness in the range of 8-13 mg of Cu,which fully conforms to market requirements.

Recipe No. 9 according to the invention, with 25% by weight of theharder cleansing agent D, forms a paste which, without additives, stillretains a tendency to flow. However, its abrasiveness, namely 16-18 mgof Cu, conforms to what is generally expected from highly-cleansingtoothpastes, for example smoker's toothpastes.

Recipe No. 12, formulated with 25% by weight of commercial cleansingagents, gives a toothpaste which does not form a stable ribbon.Moreover, even at such a high filler content, the abrasiveness, namely4-6 mg of Cu, is very low.

                                      TABLE No. 3                                 __________________________________________________________________________    Opaque dental-care compositions: Double function of cleansing agents.         Recipes without additives.                                                            Consecutive No.                                                       Recipe  1   2  3  4  5  6  7  8  9  10 11 12                                  __________________________________________________________________________    Distilled water                                                                       40.35                                                                             35.35                                                                            30.35                                                                            40.35                                                                            35.35                                                                            30.35                                                                            40.35                                                                            35.35                                                                            30.35                                                                            40.35                                                                            35.35                                                                            30.35                               Dehydazol A                                                                           1.00                                                                              →                                                                         →                                                                         →                                                                         →                                                                         →                                                                         →                                                                         →                                                                         →                                                                         →                                                                         →                                                                         →                            400 P                                                                         Solbrol M-Na                                                                          0.15                                                                              →                                                                         →                                                                         →                                                                         →                                                                         →                                                                         →                                                                         →                                                                         →                                                                         →                                                                         →                                                                         →                            Saccharin-Na                                                                          0.10                                                                              →                                                                         →                                                                         →                                                                         →                                                                         →                                                                         →                                                                         →                                                                         →                                                                         →                                                                         →                                                                         →                            Sorbitol                                                                              40.00                                                                             →                                                                         →                                                                         →                                                                         →                                                                         →                                                                         →                                                                         →                                                                         →                                                                         →                                                                         →                                                                         →                            TiO.sub.2 RN56                                                                        0.40                                                                              →                                                                         →                                                                         →                                                                         →                                                                         →                                                                         →                                                                         →                                                                         →                                                                         →                                                                         →                                                                         →                            Liquid paraffin                                                                       0.50                                                                              →                                                                         →                                                                         →                                                                         →                                                                         →                                                                         →                                                                         →                                                                         →                                                                         →                                                                         →                                                                         →                            Aromatic oil                                                                          0.50                                                                              →                                                                         →                                                                         →                                                                         →                                                                         →                                                                         →                                                                         →                                                                         →                                                                         →                                                                         →                                                                         →                            Texapon K 12                                                                          2.00                                                                              →                                                                         →                                                                         →                                                                         →                                                                         →                                                                         →                                                                         →                                                                         →                                                                         →                                                                         →                                                                         →                            Silica B                                                                              15.00                                                                             20.00                                                                            25.00                                                                            -- -- -- -- -- -- -- -- --                                  Silica C                                                                              --  -- -- 15.00                                                                            20.00                                                                            25.00                                                                            -- -- -- -- -- --                                  Silica D                                                                              --  -- -- -- -- -- 15.00                                                                            20.00                                                                            25.00                                                                            -- --                                     Silica E                                                                              --  -- -- -- -- -- -- -- -- 15.00                                                                            20.00                                                                            25.00                               Sum:    100.00                                                                            →                                                                         →                                                                         →                                                                         →                                                                         →                                                                         →                                                                         →                                                                         →                                                                         →                                                                         →                                                                         →                            __________________________________________________________________________

                  TABLE No. 4                                                     ______________________________________                                        Opaque dental-care compositions: Double function of                           cleansing agents. Results without additives.                                  Recipe/Properties                                                                              Abrasion Viscosity                                                                            Ribbon Sep-                                  Consecutive No.                                                                          pH    mg of Cu mPa.s  stability                                                                            aration                               ______________________________________                                        1          5.0   7-8      1,116  Rating 4                                                                             Rating 1                              4          5.2   8-9        930  Rating 4                                                                             Rating 1                              7          4.8   12-15      806  Rating 4                                                                             Rating 1                              10         4.1   2-3      too    Rating 4                                                                             Rating 3                                                        mobile                                              2          5.3   7-9      1,860  Rating 3                                                                             Rating 1                              5          6.2    8-11    1,736  Rating 3                                                                             Rating 1                              8          5.8   13-16    1,364  Rating 4                                                                             Rating 1                              11         4.2   2-3        868  Rating 4                                                                             Rating 3                              3          5.4    8-10    3,348  Rating 1                                                                             Rating 1                              6          5.8   11-13    2,914  Rating 1                                                                             Rating 1                              9          5.4   16-18    2,604  Rating 3                                                                             Rating 1                              12         4.0   4-6      1,860  Rating 3                                                                             Rating 1                              ______________________________________                                    

2ND SERIES OF EXAMPLES

This series of examples is intended to show that the dental-carecompositions according to the invention, containing the cleansing agentswhich are specified in more detail in the claims and have a pronounceddouble function of thickening and abrasiveness, when used together withadditives based on polyethylene glycols conform, in the case oftransparent toothpastes, to present-day market requirements in respectof abrasiveness, transparency and consistency. Commercial cleansingagents based on silica gel do not exhibit these properties, asdemonstrated by the comparative tests in the 2nd series of examples.

The composition of the transparent pastes investigated is described inmore detail in Table No. 5 (recipes 1-12).

                                      TABLE No. 5                                 __________________________________________________________________________    Transparent dental-care compositions: Double function of cleansing            agents. Recipes with additive                                                              Consecutive No.                                                  Recipe       1   2  3  4  5  6  7  8  9  10 11 12                             __________________________________________________________________________    Distilled water                                                                            17.95                                                                             17.95                                                                            12.95                                                                            12.95                                                                            17.95                                                                            17.95                                                                            12.95                                                                            12.95                                                                            17.95                                                                            17.95                                                                            12.95                                                                            12.95                          Blue dye solution                                                                          0.50                                                                              →                                                                         →                                                                         →                                                                         →                                                                         →                                                                         →                                                                         →                                                                         →                                                                         →                                                                         →                                                                         →                       Dehydazol A 400 P                                                                          0.50                                                                              →                                                                         →                                                                         →                                                                         →                                                                         →                                                                         →                                                                         →                                                                         →                                                                         →                                                                         →                                                                         →                       Solbrol M-Na 0.15                                                                              →                                                                         →                                                                         →                                                                         →                                                                         →                                                                         →                                                                         →                                                                         →                                                                         →                                                                         →                                                                         →                       Saccharin-Na 0.10                                                                              →                                                                         →                                                                         →                                                                         →                                                                         →                                                                         →                                                                         →                                                                         →                                                                         →                                                                         →                                                                         →                       Glycerol     60.00                                                                             →                                                                         →                                                                         →                                                                         →                                                                         →                                                                         →                                                                         →                                                                         →                                                                         →                                                                         →                                                                         →                       Polyethylene glycol 400                                                                    3.50                                                                              --  3.50                                                                            --  3.50                                                                            --  3.50                                                                            --  3.50                                                                            --  3.50                                                                            --                             Polyethylene glycol 1500                                                                   --   3.50                                                                            --  3.50                                                                            --  3.50                                                                            --  3.50                                                                            --  3.50                                                                            --  3.50                          Aromatic oil 1.00                                                                              →                                                                         →                                                                         →                                                                         →                                                                         →                                                                         →                                                                         →                                                                         →                                                                         →                                                                         →                                                                         →                       Texapon K 12 1.30                                                                              →                                                                         →                                                                         →                                                                         →                                                                         →                                                                         →                                                                         →                                                                         →                                                                         →                                                                         →                                                                         →                       Silica A     15.00                                                                             15.00                                                                            20.00                                                                            20.00                                                                            -- -- -- -- -- -- -- --                             Silica C     --  -- -- -- 15.00                                                                            15.00                                                                            20.00                                                                            20.00                                                                            -- -- -- --                             Silica E     --  -- -- -- -- -- -- -- 15.00                                                                            15.00                                                                            20.00                                                                            20.00                          Sum:         100.00                                                                            →                                                                         →                                                                         →                                                                         →                                                                         →                                                                         →                                                                         →                                                                         →                                                                         →                                                                         →                                                                         →                       __________________________________________________________________________                                                   2                          

                                      TABLE No. 6                                 __________________________________________________________________________     Transparent dental-care compositions: Double function of cleansing           agents with additive                                                          Results                                                                       Recipe     Abrasion                                                                           Viscosity                                                     Consecutive No.                                                                        pH                                                                              mg of Cu                                                                           mPa.s   Ribbon stability                                                                      Separation                                                                          Transparency                            __________________________________________________________________________    1        7.6                                                                             16   1,100   Rating 4                                                                              Rating 1                                                                            Rating 2                                5        7.8                                                                             14   1,302   Rating 4                                                                              Rating 1                                                                            Rating 2                                9        5.9                                                                              7   not measurable                                                                        Rating 4                                                                              Rating 4                                                                            Rating 4                                2        7.2                                                                             15   1,320   Rating 3                                                                              Rating 1                                                                            Rating 2                                6        7.9                                                                             12   1,612   Rating 3                                                                              Rating 1                                                                            Rating 2                                10       6.0                                                                              5   not measurable                                                                        Rating 4                                                                              Rating 4                                                                            Rating 4                                3        7.5                                                                             18   1,980   Rating 3                                                                              Rating 1                                                                            Rating 2                                7        7.7                                                                             14   2,480   Rating 2                                                                              Rating 1                                                                            Rating 2                                11       5.8                                                                              6     868   Rating 4                                                                              Rating 1                                                                            Rating 4                                4        7.4                                                                             17   2,980   Rating 1                                                                              Rating 1                                                                            Rating 2                                8        7.7                                                                             13   3,410   Rating 1                                                                              Rating 1                                                                            Rating 2                                12       5.8                                                                              6   1,550   Rating 3                                                                              Rating 1                                                                            Rating 4                                __________________________________________________________________________

Table No. 6 shows the results (pH, Cu abrasion, viscosity, ribbonstability, separation and transparency) of the measurements carried outon recipes 1-12. It follows that:

Recipes No. 4 and No. 8 according to the invention, containing 20% byweight of cleansing agents A and C respectively and 3.5% of polyethyleneglycol 1,500, give toothpastes which produce stable ribbons and have anabrasiveness which fully conforms to market requirements.

Recipes No. 11 and No. 12, formulated with 20% by weight of commercialcleansing agents, do not form stable-ribbon toothpastes either with 3.5%of polyethylene glycol 400 or with polyethylene glycol 1,500. Thetransparency of these pastes is also unsatisfactory.

3RD SERIES OF EXAMPLES

This series of examples is intended to demonstrate that the dental-carecomposition according to the invention containing the cleansing agentswhich have the double function of thickening and abrasiveness, togetherwith additives based on polyethylene glycols, conform to present-daymarket requirements in respect of abrasiveness and consistency and areeven superior in respect of the amount of cleansing agent to beemployed.

Commercial cleansing agents based on silica gel do not exhibit thisproperty even in the presence of 5% of polyethylene glycol 1,500, as isdemonstrated by the comparative tests of the 3rd series of examples.

The composition of the opaque pastes investigated is described in moredetail in Table No. 7 (recipes 1-12).

Table No. 8 gives the results (pH, Cu abrasion, viscosity, ribbonstability and separation) of the measurements carried out on recipes1-12. It follows from these that:

Recipes No. 4, No. 7 and No. 8 according to the invention, containing20% by weight of cleansing agent A or C and 2% by weight or 5% by weightof polyethylene glycol 1,500, from stable-ribbon toothpastes whoseabrasiveness fully conforms to market requirements.

Recipes No. 9, No. 10, No. 11 and No. 12, formulated with 20% by weightof commercial cleansing agents, do not form stable-ribbon toothpasteseither with 2% by weight or with 5% by weight of polyethylene glycol 400or polyethylene glycol 1,500.

                                      TABLE No. 7                                 __________________________________________________________________________    Opaque dental-care compositions: Double function of cleansing agents.         Recipes with additive                                                                      Consecutive No.                                                  Recipe       1   2  3  4  5  6  7  8  9  10 11 12                             __________________________________________________________________________    Distilled water                                                                            33.35                                                                             30.35                                                                            33.35                                                                            30.35                                                                            33.35                                                                            30.35                                                                            33.35                                                                            30.35                                                                            33.35                                                                            30.35                                                                            33.35                                                                            30.35                          Dehydazol A 400P                                                                           1.00                                                                              →                                                                         →                                                                         →                                                                         →                                                                         →                                                                         →                                                                         →                                                                         →                                                                         →                                                                         →                                                                         →                       Solbrol M-Na 0.15                                                                              →                                                                         →                                                                         →                                                                         →                                                                         →                                                                         →                                                                         →                                                                         →                                                                         →                                                                         →                                                                         →                       Saccharin-Na 0.10                                                                              →                                                                         →                                                                         →                                                                         →                                                                         →                                                                         →                                                                         →                                                                         →                                                                         →                                                                         →                                                                         →                       Sorbitol     40.00                                                                             →                                                                         →                                                                         →                                                                         →                                                                         →                                                                         →                                                                         →                                                                         →                                                                         →                                                                         →                                                                         →                       Polyethylene glycol 400                                                                    2.00                                                                               5.00                                                                            -- --  2.00                                                                             5.00                                                                            -- --  2.00                                                                             5.00                                                                            -- --                             Polyethylene glycol 1500                                                                   --  --  2.00                                                                             5.00                                                                            -- --  2.00                                                                             5.00                                                                            -- --  2.00                                                                             5.00                          TiO.sub.2 RN 56                                                                            0.40                                                                              →                                                                         →                                                                         →                                                                         →                                                                         →                                                                         →                                                                         →                                                                         →                                                                         →                                                                         →                                                                         →                       Liquid paraffin                                                                            0.50                                                                              →                                                                         →                                                                         →                                                                         →                                                                         →                                                                         →                                                                         →                                                                         →                                                                         →                                                                         →                                                                         →                       Aromatic oil 0.50                                                                              →                                                                         →                                                                         →                                                                         →                                                                         →                                                                         →                                                                         →                                                                         →                                                                         →                                                                         →                                                                         →                       Texapon K 12 2.00                                                                              →                                                                         →                                                                         →                                                                         →                                                                         →                                                                         →                                                                         →                                                                         →                                                                         →                                                                         →                                                                         →                       Silica A     20.00                                                                             20.00                                                                            20.00                                                                            20.00                                                                            -- -- -- -- -- -- -- --                             Silica C     --  -- -- -- 20.00                                                                            20.00                                                                            20.00                                                                            20.00                                                                            -- -- -- --                             Silica E     --  -- -- -- -- -- -- -- 20.00                                                                            20.00                                                                            20.00                                                                            20.00                          Sum:         100.00                                                                            →                                                                         →                                                                         →                                                                         →                                                                         →                                                                         →                                                                         →                                                                         →                                                                         →                                                                         →                                                                         →                       __________________________________________________________________________

                  TABLE No. 8                                                     ______________________________________                                        Opaque dental-care compositions: Double                                       function of cleansing agents with additive.                                   Results                                                                       Recipe           Abrasion Viscosity                                                                            Ribbon Sep-                                  Consecutive No.                                                                          pH    mg of Cu mPa.s  stability                                                                            aration                               ______________________________________                                        1          5.6   13       1,860  Rating 3                                                                             Rating 1                              5          5.9   12       2,348  Rating 2                                                                             Rating 1                              9          4.0    5       1,040  Rating 4                                                                             Rating 1                              2          5.7   12       2,120  Rating 2                                                                             Rating 1                              6          5.5   10       2,506  Rating 2                                                                             Rating 1                              10         4.1    4       1,320  Rating 3                                                                             Rating 1                              3          5.5   15       2,450  Rating 2                                                                             Rating 1                              7          5.8   12       2,640  Rating 1                                                                             Rating 1                              11         4.0    6       1,220  Rating 3                                                                             Rating 1                              4          5.6   14       3,120  Rating 1                                                                             Rating 1                              8          5.9   13       3,320  Rating 1                                                                             Rating 1                              12         4.1    6       1,580  Rating 3                                                                             Rating 1                              ______________________________________                                    

4TH SERIES OF EXAMPLES

The series of examples which follows is intended to demonstrate themarked superiority of the cleansing agents used in the dental-carecompositions according to the invention, in respect of their abrasionand also of their thickening action, compared to commercial cleansingagents based on silica gels. In order to highlight the differences moreclearly, use is made of a thickening precipitated silica, for example FK320 DS. The test results show that, at a constant degree of filling of22% by weight, the abrasive action and thickening action in thedental-care composition according to the invention can be varied by thechoice of the ratio of abrasive component to thickening component. Bycomparison, this variability is very greatly restricted when usingcommercial cleansing agents.

The composition of the opaque toothpastes investigated is described inmore detail in Table No. 9 (recipes 1-20).

Table No. 10 contains the results (pH, Cu abrasion and viscosity) of themeasurements carried out on recipes 1-20. The conclusion for recipes1-10 are as follows:

Recipes No. 1-No. 5 according to the invention, having a total silicacontent of 22% by weight, in every case conform to what the marketrequires of a dental-care composition. This is also true of thoseformulations which contain either none, or only 2% by weight, of athickening precipitated silica (type G). On increasing the content ofthickening component while at the same time lowering the content ofcleansing agent (type G), the toothpastes obtained give very stableribbons and, because of their relatively high viscosity, permit savingsof thickening silica. In contrast, recipes No. 8-No. 10, tested forcomparison and having the same total silica content, but containingcleansing agent type E, are insufficiently viscous. Only with recipesNo. 6 and No. 7, which contain 12 and 14% by weight of thickening silica(type G), are toothpastes with an acceptable consistency obtained.

In recipes No. 1-No. 5 according to the invention, and also incomparative recipes No. 6-No. 10, the abrasiveness does not increaselinearly with increasing content of cleansing agent type C or type E.However, the increase in abrasiveness, viewed in absolute terms, isgreater in the recipes according to the invention, containing cleansingagent of type C, than in the comparative recipes, containing thecommercial cleansing agent of type E.

As regards the results, shown in Table No. 10, of the measurements onrecipes No. 11-No. 20, the conclusions are:

Recipes No. 11-No. 20 according to the invention, having a total silicacontent of 22% by weight, substantially conform to what the marketrequires of a dental-care composition. Formulations No. 14, No. 15, No.19 and No. 20, which contain none, or only 2% by weight, of a thickeningprecipitated silica (type G), tend to flow. On increasing the content ofthickener component, while at the same time lowering the content ofcleansing agent component (types A and D), toothpastes are obtainedwhich give very stable ribbons and whose recipes, because of theirrelatively high level of thickening, permit savings of thickeningsilica.

In the cleansing agents according to the invention, of type A and typeD, Cu abrasion values in the range of 11-18 mg of Cu can be obtained,made-to-measure, depending on the composition of the recipes in respectof abrasive component and thickening component. Even in the extreme casewhere only abrasive component is used, the ribbon stability remainsgood. However, it is found that the Cu abrasion values increase far fromlinearly with the concentration of the abrasive component while on theother hand the abrasiveness of the dental-care compositions according tothe invention can be selected within relatively wide limits withouthaving to sacrifice other important properties of the composition, suchas ribbon stability and separation stability. This is not true whenusing the commercial cleansing agent (type E) based on silica gel.

                                      TABLE No. 9                                 __________________________________________________________________________    Opaque dental-care compositions: Double function of cleansing agents.         Recipes contain precipitated silicas having a thickening                      __________________________________________________________________________    action.                                                                                 Consecutive No.                                                     Recipe    1   2  3  4  5  6  7  8  9  10                                      __________________________________________________________________________    Distilled water                                                                         33.40                                                                             →                                                                         →                                                                         →                                                                         →                                                                         →                                                                         →                                                                         →                                                                         →                                                                         →                                Dehydazol A 400P                                                                        1.00                                                                              →                                                                         →                                                                         →                                                                         →                                                                         →                                                                         →                                                                         →                                                                         →                                                                         →                                Solbrol M 0.15                                                                              →                                                                         →                                                                         →                                                                         →                                                                         →                                                                         →                                                                         →                                                                         →                                                                         →                                Saccharin-Na                                                                            0.05                                                                              →                                                                         →                                                                         →                                                                         →                                                                         →                                                                         →                                                                         →                                                                         →                                                                         →                                Sorbitol  30.00                                                                             →                                                                         →                                                                         →                                                                         →                                                                         →                                                                         →                                                                         →                                                                         →                                                                         →                                Glycerol  10.00                                                                             →                                                                         →                                                                         →                                                                         →                                                                         →                                                                         →                                                                         →                                                                         →                                                                         →                                TiO.sub.2 RN 56                                                                         0.40                                                                              →                                                                         →                                                                         →                                                                         →                                                                         →                                                                         →                                                                         →                                                                         →                                                                         →                                Liquid paraffin                                                                         0.50                                                                              →                                                                         →                                                                         →                                                                         →                                                                         →                                                                         →                                                                         →                                                                         →                                                                         →                                Aromatic oil                                                                            0.50                                                                              →                                                                         →                                                                         →                                                                         →                                                                         →                                                                         →                                                                         →                                                                         →                                                                         →                                Texapon K 12                                                                            2.00                                                                              →                                                                         →                                                                         →                                                                         →                                                                         →                                                                         →                                                                         →                                                                         →                                                                         →                                Silica C  8.00                                                                              10.00                                                                            14.00                                                                            20.00                                                                            22.00                                                                            -- -- -- -- --                                      Silica E  --  -- -- -- --  8.00                                                                            10.00                                                                            14.00                                                                            20.00                                                                            22.00                                   Silica G  14.00                                                                             12.00                                                                             8.00                                                                             2.00                                                                            -- 14.00                                                                            12.00                                                                             8.00                                                                             2.00                                                                            --                                      Sum:      100.00                                                                            →                                                                         →                                                                         →                                                                         →                                                                         →                                                                         →                                                                         →                                                                         →                                                                         →                                __________________________________________________________________________              Consecutive No.                                                     Recipe    11  12 13 14 15 16 17 18 19 20                                      __________________________________________________________________________    Distilled water                                                                         33.40                                                                             →                                                                         →                                                                         →                                                                         →                                                                         →                                                                         →                                                                         →                                                                         →                                                                         →                                Dehydazol A 400P                                                                        1.00                                                                              →                                                                         →                                                                         →                                                                         →                                                                         →                                                                         →                                                                         →                                                                         →                                                                         →                                Solbrol M 0.15                                                                              →                                                                         →                                                                         →                                                                         →                                                                         →                                                                         →                                                                         →                                                                         →                                                                         →                                Saccharin-Na                                                                            0.05                                                                              →                                                                         →                                                                         →                                                                         →                                                                         →                                                                         →                                                                         →                                                                         →                                                                         →                                Sorbitol  30.00                                                                             →                                                                         →                                                                         →                                                                         →                                                                         →                                                                         →                                                                         →                                                                         →                                                                         →                                Glycerol  10.00                                                                             →                                                                         →                                                                         →                                                                         →                                                                         →                                                                         →                                                                         →                                                                         →                                                                         →                                TiO.sub.2 RN 56                                                                         0.40                                                                              →                                                                         →                                                                         →                                                                         →                                                                         →                                                                         →                                                                         →                                                                         →                                                                         →                                Liquid paraffin                                                                         0.50                                                                              →                                                                         →                                                                         →                                                                         →                                                                         →                                                                         →                                                                         →                                                                         →                                                                         →                                Aromatic oil                                                                            0.50                                                                              →                                                                         →                                                                         →                                                                         →                                                                         →                                                                         →                                                                         →                                                                         →                                                                         →                                Texapon K 12                                                                            2.00                                                                              →                                                                         →                                                                         →                                                                         →                                                                         →                                                                         →                                                                         →                                                                         →                                                                         →                                Silica A  8.00                                                                              10.00                                                                            14.00                                                                            20.00                                                                            22.00                                                                            -- -- -- -- --                                      Silica D  --  -- -- -- --  8.00                                                                            10.00                                                                            14.00                                                                            20.00                                                                            22.00                                   Silica G  14.00                                                                             12.00                                                                             8.00                                                                             2.00                                                                            -- 14.00                                                                            12.00                                                                             8.00                                                                             2.00                                                                            --                                      Sum:      100.00                                                                            →                                                                         →                                                                         →                                                                         →                                                                         →                                                                         →                                                                         →                                                                         →                                                                         →                                __________________________________________________________________________

                  TABLE No. 10                                                    ______________________________________                                        Opaque dental-care compositions: Double function of cleansing                 agents. Recipes contain precipitated silicas having a                         thickening action.                                                            Results                                                                       Recipe           Abrasion  Viscosity                                                                            Assessment of                               Consecutive No.                                                                          pH    mg of Cu  mPa.s  ribbon stability                            ______________________________________                                         1         4.9   8-9       6,000  Rating 1                                     2         5.2    9-11     5,270  Rating 1                                     3         5.3   10-12     4,650  Rating 1                                     4         5.5   13-14     3,800  Rating 1                                     5         5.4   13-15     3,100  Rating 1                                     6         4.4   2-3       5,200  Rating 1                                     7         4.2   2-3       3,400  Rating 1                                     8         4.2   3-4       2,700  Rating 2                                     9         4.1   5         1,800  Rating 3                                    10         4.2   5-6       1,300  Rating 4                                    11         5.0   11-13     5,952  Rating 1                                    12         5.2   10-12     5,230  Rating 1                                    13         5.5   12-14     4,430  Rating 1                                    14         5.0   13-15     3,100  Rating 2                                    15         5.5   16-18     2,840  Rating 2                                    16         5.0   12-14     5,890  Rating 1                                    17         5.0   14-16     4,960  Rating 1                                    18         5.1   15-17     4,340  Rating 1                                    19         5.4   16-18     2,914  Rating 2                                    20         5.0   16-18     2,790  Rating 2                                    ______________________________________                                    

5TH SERIES OF EXAMPLES

The series of examples which follows is intended to provide experimentalproof that the use of a few percent of thickening pyrogenic silica, eg.Aerosil®200V, in combination with the cleansing agents used in thedental-care compositions according to the invention gives toothpasteswhich in respect of abrasion and thickening characteristics are entirelycomparable with commercial dental-care compositions now on the market.

The series of examples also shows that by the use of pyrogenic silicas,as components which help determine the rheology, the total content ofsilica filler can be markedly reduced.

The composition of the opaque toothpastes investigated is shown in moredetail in Table No. 11 (recipes No. 1-No. 4).

Table No. 12 contains the results (pH, Cu abrasion and viscosity) of themeasurements on recipes No. 1-No. 4. It follows from these that:

Using the pyrogenic silica Aerosil®200V as a thickening silica, thetotal silica content in an opaque dental-care composition according tothe invention can be reduced by 17% by weight if, at the same time, 14%by weight of cleansing agent C and 3% by weight of thickening silica oftype H are employed. In that case, the characteristics of a commercialopaque toothpaste, in respect of abrasion and rheological properties,are obtained.

                  TABLE No. 11                                                    ______________________________________                                        Opaque dental-care compositions: Double function of cleansing                 agents. Recipes contain pyrogenic silica having a thickening action.                       Consecutive No.                                                  Recipe         1       2         3    4                                       ______________________________________                                        Distilled water                                                                              35.35   37.35     38.35                                                                              38.35                                   Dehydazol A 400 P                                                                            1.00    →  →                                                                           →                                Solbrol M      0.15    →  →                                                                           →                                Saccharin      0.10    →  →                                                                           →                                Sorbitol       40.00   →  →                                                                           →                                TiO.sub.2 RN 56                                                                              0.40    →  →                                                                           →                                Liquid paraffin                                                                              0.50    →  →                                                                           →                                Aromatic oil   0.50    →  →                                                                           →                                Texapon K 12   2.00    →  →                                                                           →                                Silica C       18.00   16.00     15.00                                                                              14.00                                   Silica H       2.00     2.00      2.00                                                                               3.00                                   Sum            100.    →  →                                                                           →                                ______________________________________                                    

                  TABLE No. 12                                                    ______________________________________                                        Opaque dental-care compositions: Double function of cleansing                 agents. Recipes contain pyrogenic silica having a thickening action.          Results                                                                       Recipe           Abrasion  Viscosity                                                                            Assessment of                               Consecutive No.                                                                          pH    mg of Cu  mPa.s  ribbon stability                            ______________________________________                                        1          5.4   10-11     2,420  Rating 2                                    2          5.2   9-10      2,170  Rating 3                                    3          5.4   9-10      1,800  Rating 3                                    4          5.0   8-10      2,728  Rating 1                                    ______________________________________                                    

6TH SERIES OF EXAMPLES

This series of examples serves to show the superiority of the noveldental-care composition, in respect of shelf life, in comparison withthe commercial toothpastes wherein the cleaning agents are based onsilica xerogels, chalk and phosphate derivatives.

The examples are intended to demonstrate the very important property ofshelf life in respect of the variation of rheological properties withtime (after-thickening is a phenomenon to be feared) and also in respectof the dependence of abrasiveness on time.

The opaque and transparent toothpastes prepared for the storage tests,as well as the chalk and phosphate toothpastes considered forcomparative purposes are shown, in respect of their composition, inTables No. 13-No. 16.

The results of the shelf life test, which extended over 12 months, aresummarized, for all the systems investigated, in Tables No. 17-No. 20.

                  TABLE No. 13                                                    ______________________________________                                        Opaque dental-care compositions (containing silica).                          Recipes for testing the shelf life.                                                      Consecutive No.                                                    Recipe       1       2      3    4     5    6                                 ______________________________________                                        Distilled water                                                                            35.35   →                                                                             →                                                                           →                                                                            →                                                                           →                          Dehydazol A 400 P                                                                          1.00    →                                                                             →                                                                           →                                                                            →                                                                           →                          Solbrol M    0.15    →                                                                             →                                                                           →                                                                            →                                                                           →                          Saccharin    0.10    →                                                                             →                                                                           →                                                                            →                                                                           →                          Sorbitol     40.00   →                                                                             →                                                                           →                                                                            →                                                                           →                          TiO.sub.2 RN 56                                                                            0.40    →                                                                             →                                                                           →                                                                            →                                                                           →                          Liquid paraffin                                                                            0.50    →                                                                             →                                                                           →                                                                            →                                                                           →                          Aromatic oil 0.50    →                                                                             →                                                                           →                                                                            →                                                                           →                          Texapon K 12 2.00    →                                                                             →                                                                           →                                                                            →                                                                           →                          Silica A     10.00   --     --   --    --   --                                Silica B     --      10.00  --   --    --   --                                Silica C     --      --     10.00                                                                              --    --   --                                Silica D     --      --     --   10.00 --   --                                Silica E     --      --     --   --    10.00                                                                              --                                Silica F     --      --     --   --    --   10.00                             Silica G     10.00   →                                                                             →                                                                           →                                                                            →                                                                           →                          Sum:         100.00  →                                                                             →                                                                           →                                                                            →                                                                           →                          ______________________________________                                    

                  TABLE No. 14                                                    ______________________________________                                        Transparent dental-care compositions (containing silica).                     Recipes for testing the shelf life.                                                       Consecutive No.                                                   Recipe        1        2      3     4    5                                    ______________________________________                                        Distilled water                                                                             12.95    →                                                                             →                                                                            →                                                                           →                             Dehydazol A 400 P                                                                           0.50     →                                                                             →                                                                            →                                                                           →                             Solbrol M--Na 0.15     →                                                                             →                                                                            →                                                                           →                             0.5% dye solution                                                                           0.50     →                                                                             →                                                                            →                                                                           →                             Saccharin-Na  0.10     →                                                                             →                                                                            →                                                                           →                             Glycerol      60.00    →                                                                             →                                                                            →                                                                           →                             Polyethylene glycol 400                                                                     3.50     →                                                                             →                                                                            →                                                                           →                             Aromatic oil  1.00     →                                                                             →                                                                            →                                                                           →                             Texapon K 12  1.30     →                                                                             →                                                                            →                                                                           →                             Silica A      10.00    --     --    --   --                                   Silica C      --       10.00  --    --   --                                   Silica D      --       --     10.00 --   --                                   Silica E      --       --     --    10.00                                                                              --                                   Silica F      --       --     --    --   10.00                                Silica G      10.00    →                                                                             →                                                                            →                                                                           →                             Sum           100.00   →                                                                             →                                                                            →                                                                           →                             ______________________________________                                    

                  TABLE No. 15                                                    ______________________________________                                        Dental-care composition based on chalk.                                       Recipe for testing the shelf life.                                            Recipe          Consecutive No. 1                                             ______________________________________                                        Distilled water 41.05                                                         Dehydazol A 400 P                                                                             1.00                                                          Solbrol M       0.15                                                          Saccharin       0.25                                                          Glycerol        20.00                                                         Aromatic oil    1.75                                                          Texapon K 12    4.00                                                          Chalk           29.80                                                         Silica H        2.00                                                          Sum:            100.00                                                        ______________________________________                                    

                  TABLE No. 16                                                    ______________________________________                                        Dental-care composition based on dicalcium phosphate                          dihydrate. Recipe for testing the shelf life.                                 Recipe                  Consecutive No. 1                                     ______________________________________                                        Distilled water         29.00                                                 Dehydazol A 400 P       0.80                                                  Solbrol M-Na            0.15                                                  Saccharin-Na            0.05                                                  Sorbitol                20.00                                                 Glycerol                5.00                                                  Aromatic oil            0.50                                                  Texapon K 12            2.00                                                  Dicalcium phosphate dihydrate (Dentphos)                                                              41.00                                                 Silica H                1.50                                                  Sum:                    100.00                                                ______________________________________                                    

                                      TABLE NO. 17                                __________________________________________________________________________    Opaque silica-containing dental-care composition. Shelf life results          Recipe                                                                        Consecutive       Storage time:                                               No.    Properties immediate                                                                           1 month                                                                            3 months                                                                           6 months                                                                           9 months                                                                           12 months                         __________________________________________________________________________    1      Abrasion (mg of Cu)                                                                      13    12   12   12   12   13                                       Viscosity (mPa.s)                                                                        10,100                                                                              9,600                                                                              10,300                                                                             10,500                                                                             10,750                                                                             10,900                            2      Abrasion (mg of Cu)                                                                       5     6   7                                                       Viscosity (mPa.s)                                                                        12,240                                                                              11,850                                                                             10,500                                           3      Abrasion (mg of Cu)                                                                      11    10   9                                                       Viscosity (mPa.s)                                                                        11,016                                                                              10,890                                                                             10,240                                           4      Abrasion (mg of Cu)                                                                      13    14   12                                                      Viscosity (mPa.s)                                                                         9,180                                                                              9,220                                                                              10,100                                           5      Abrasion (mg of Cu)                                                                       3     4   5    5    7     8                                       Viscosity (mPa.s)                                                                         9,400                                                                              6,800                                                                               5,500                                                                             4,800                                                                              3,950                                                                              2,800                             6      Abrasion (mg of Cu)                                                                       6     7   8    8    9    11                                       Viscosity (mPa.s)                                                                         8,600                                                                              7,100                                                                               6,500                                                                             5,800                                                                              3,500                                                                              2,170                             __________________________________________________________________________

                                      TABLE NO. 18                                __________________________________________________________________________    Transparent silica-containing dental-care composition. Shelf life             results                                                                       Recipe                                                                        Consecutive       Storage time:                                               No.    Properties immediate                                                                           1 month                                                                            3 months                                                                           6 months                                                                           9 months                                                                           12 months                         __________________________________________________________________________    1      Abrasion (mg of Cu)                                                                      12    13   13   14   12   14                                       Viscosity (mPa.s)                                                                        10,000                                                                              9,800                                                                              9,500                                                                              10,200                                                                             10,500                                                                             10,100                            2      Abrasion (mg of Cu)                                                                      12    11   13                                                      Viscosity (mPa.s)                                                                        12,900                                                                              12,500                                                                             11,500                                           3      Abrasion (mg of Cu)                                                                      14    13   12                                                      Viscosity (mPa.s)                                                                        11,300                                                                              10,800                                                                             11,200                                           4      Abrasion (mg of Cu)                                                                       6     6    6   10   11   12                                       Viscosity (mPa.s)                                                                         9,800                                                                              7,800                                                                              7,500                                                                              4,900                                                                              3,900                                                                              2,800                             5      Abrasion (mg of Cu)                                                                      12    16   17   17   19   20                                       Viscosity (mPa.s)                                                                         9,800                                                                              8,500                                                                              6,300                                                                              4,700                                                                              2,950                                                                              2,300                             __________________________________________________________________________

                                      TABLE NO. 19                                __________________________________________________________________________    Dental-care composition based on chalk. Shelf life results                    Recipe                                                                        Consecutive       Storage time:                                               No.    Properties immediate                                                                           1 month                                                                            3 months                                                                           6 months                                                                           9 months                                                                           12 months                         __________________________________________________________________________    1      Abrasion (mg of Cu)                                                                      8     9    10   10   9    8                                        Viscosity (mPa.s)                                                                        6,450 6,800                                                                              4,200                                                                              4,500                                                                              3,900                                                                              3,600                             __________________________________________________________________________

                                      TABLE NO. 20                                __________________________________________________________________________    Dental-care composition based on dicalcium phosphate dihydrate. Shelf         life results                                                                  Recipe                                                                        Consecutive       Storage time:                                               No.    Properties immediate                                                                           1 month                                                                            3 months                                                                           6 months                                                                           9 months                                                                           12 months                         __________________________________________________________________________    1      Abrasion (mg of Cu)                                                                      3     3    4    3    2    3                                        Viscosity (mPa.s)                                                                        9,350 9,100                                                                              8,150                                                                              6,350                                                                              4,050                                                                              3,000                             __________________________________________________________________________

The following relationships can be demonstrated:

The dental-care compositions according to the invention (see Table No.17, recipes No. 1-No. 4 and Table No. 18, recipes No. 1-No. 3), whichcontain, respectively, cleansing agents A, B, C and D and cleansingagents A, C and D, surprisingly show an exceptional shelf life. This istrue both of the abrasiveness and the viscosity characteristics inopaque and in transparent toothpastes. In practical terms, this resultmeans that the abrasiveness determined at the final quality control ofthe product also applies after the product has been stored by theconsumer, and that neither does the greatly feared after-thickeningoccur, causing the toothpaste to be unusable by the consumer, nor doesdiminishing viscosity cause the requisite ribbon stability to disappearand bring about the disliked phenomenon of separation.

The dental-care compositions which are employed for comparison and whichcontain the commercial cleansing agents E and F, based on silica gel(see Table No. 17, recipe No. 5 and No. 6, and Table No. 18, recipe No.4 and No. 5) show after one year's storage, both in the case of opaqueand of transparent systems, a great increase in abrasiveness (80-165%?)and a great decrease in initial viscosity (down to 23%), which markedlylower the quality of these dental-care compositions. Accordingly, suchcompositions are not storage-stable over the chosen period ofinvestigation.

The dental-care compositions, also employed for comparative purposes,which contain chalk or dicalcium phosphate dihydrate as commercialcleansing agents (cf. Tables No. 19 and No. 20) admittedly retain theirabrasiveness over a period of one year's storage, but in these systemsagain, a marked decrease of the initial viscosity is observed, thisbeing somewhat more pronounced (down to 32%) in phosphate-containingpastes than in chalk-containing pastes (down to 56%). Accordingly, thesedental-care compositions can also not be regarded as storage-stable overthe chosen period of investigation.

The patents and patent applications identified above are relied on andincorporated herein by reference.

We claim:
 1. A transparent dental-care toothpaste composition having asmooth, speck-free and glossy ribbon as well as improved shelf life inrespect of rheology and abrasiveness, which comprises a sufficientamount of water, an abrasive agent which is a precipitated silicacharacterized by the following physicochemical properties:

    ______________________________________                                        BET surface area determined                                                                       m.sup.2 /g                                                                             15-110                                           according to DIN 66,131                                                       Tamped density      g/l      150-750                                          Secondary particle size                                                                           according to FIG. 1                                       distribution curve according                                                  to Coulter counter                                                            "ALPINE" screen retainings                                                                        % by     <1.5                                             >63 μm           weight                                                    Cu abrasion in 10% strength                                                                       mg       5-30                                             glycerol dispersion                                                           Viscosity of a 30% strength                                                                       mPa.s    30,000-60,000                                    dispersion in a 1:1 water/                                                    glycerol mixture (Brookfield                                                  RTV Sp 5)                                                                     Lightness value A according to                                                                    %        86-96                                            DIN 55,921                                                                    ______________________________________                                    

and an additional precipitated silica.
 2. A transparent dental-caretoothpaste composition having a smooth, speck-free and glossy ribbon aswell as improved shelf life in respect of rheology and abrasiveness,which comprises a sufficient amount of water, a precipitated silicathickening agent and an abrasive agent which is a precipitated silicacharacterized by the following physico-chemical properties:

    ______________________________________                                        BET surface area determined                                                                       m.sup.2 /g                                                                             15-110                                           according to DIN 66,131                                                       Tamped density      g/l      150-750                                          Secondary particle size                                                                           according to FIG. 1                                       distribution curve according                                                  to Coulter counter                                                            "ALPINE" screen retainings                                                                        % by     <1.5                                             >63 μm           weight                                                    Cu abrasion in 10% strength                                                                       mg       5-30                                             glycerol dispersion                                                           Viscosity of a 30% strength                                                                       mPa.s    30,000-60,000                                    dispersion in a 1:1 water/                                                    glycerol mixture (Brookfield                                                  RTV Sp 5)                                                                     Lightness value A according to                                                                    %        86-96                                            DIN 55,921                                                                    ______________________________________                                    

wherein said precipitated silica abrasive agent is prepared by providingan initial alkali metal silicate solution having a concentration ofabout 5-25 g of SiO₂ per liter of solution and adding thereto an acidand alkali metal silicate solution of particular concentrations, atparticular feed rates, while maintaining a precipitation temperature inthe reaction medium between 80° and 90° C., the precipitation beingcarried out under such conditions that the viscosity of the reactionmedium is kept, for at least 30% of the total precipitation time, at auniform low value while the pH is kept between 10 and 12, and theaddition of the reactants only being terminated when the viscosity,after passing through a maximum, has dropped to a value which is lessthan 100% above the initial value to obtain an initial suspension ofprecipitated silica, thereafter diluting the initial suspension ofprecipitated silica with hot water to provide a precipitated silicacontent of 10-30 g/l and a sodium sulfate content of 6-20 g/l thetemperature being maintained at 85° -95° C., the pH being brought to 7-9with the addition of sulfuric acid and while keeping the pH valueconstant, adding alkali metal silicate solution, sulfuric acid and hotwater simultaneously over a precipitation period of 30-180 minutes togive a final concentration of precipitated silica of 40-80 g/l, thesuspension being then acified with concentrated sulfuric acid to a pHbelow 7, separating the precipitated silica from the suspension by meansof a filter press, washing, drying and thereafter milling with apendulum roller mill.
 3. A transparent dental-care toothpastecomposition having a smooth, speck free and glossy ribbon as well asimproved shelf life in respect of rheology and abrasiveness, whichcomprises a sufficient amount of water, an abrasive agent which is asufficient amount of a precipitated silica characterized by thefollowing physicochemical properties:

    ______________________________________                                        BET surface area determined                                                                      m.sup.2 /g                                                                            15-110                                             according to DIN 66,131                                                       Tamped density     g/l     90-650                                             Secondary particle size                                                                          according to FIG. 2                                        distribution curve accord-                                                    ing to Coulter counter                                                        "ALPINE" screen retainings                                                                       % by    <0.1                                               >63 μm          weight                                                     Cu abrasion in 10% strength                                                                      mg      5-30                                               glycerol dispersion                                                           Viscosity of a 30% strength                                                                      mPa · s                                                                      30,000-60,000                                      dispersion in a 1:1 water/                                                    glycerol mixture (Brookfield                                                  RTV Sp 5)                                                                     Lightness value A  %       90-96                                              according to DIN 55,921                                                       ______________________________________                                    


4. A transparent dental-care toothpaste composition having a smooth,speck free and glossy ribbon as well as improved shelf life in respectof rheology and abrasiveness, which comprises a sufficient amount ofwater, a precipitated silica thickening agent, an abrasive agent whichis a sufficient amount of a precipitated silica characterized by thefollowing physicochemical properties:

    ______________________________________                                        BET surface area determined                                                                      m.sup.2 /g                                                                            15-110                                             according to DIN 66,131                                                       Tamped density     g/l     90-650                                             Secondary particle size                                                                          according to FIG. 2                                        distribution curve accord-                                                    ing to Coulter counter                                                        "ALPINE" screen retainings                                                                       % by    <0.1                                               >63 μm          weight                                                     Cu abrasion in 10% strength                                                                      mg      5-30                                               glycerol dispersion                                                           Viscosity of a 30% strength                                                                      mPa · s                                                                      30,000-60,000                                      dispersion in a 1:1 water/                                                    glycerol mixture (Brookfield                                                  RTV Sp 5)                                                                     Lightness value A  %       90-96                                              according to DIN 55,921                                                       ______________________________________                                    

wherein said precipitated silica is prepared by providing an initialalkali metal silicate solution having a concentration of about 5-25 g ofSiO₂ per liter of solution and adding thereto an acid and alkali metalsilicate solution while maintaining a precipitation temperature in thereaction medium between 80° and 90° C., the precipitation being carriedout under such conditions that the pH is kept between 10 and 12, theviscosity of the reaction medium being at a uniform low value for atleast 30% of the total precipitation time, and terminating the additionof the reactants when the viscosity of the reaction medium, afterpassing through a maximum, falls to a value which is less than 100%above the initial value to thereby obtain a silica suspension,thereafter diluting the suspension of precipitated silica with hot waterto form a precipitated silica content of 10-30 g/l and a sodium sulfatecontent of 6 to 20 g/l, heating to a temperature of 85°-95°, acidifyingwith the addition of sulfuric acid to a pH value of 7 to 9, and whilekeeping the pH value constant, adding alkali metal silicate solution,sulfuric acid and hot water simultaneously over a precipitation periodof 30-180 minutes to provide a final concentration of precipitatedsilica of 40-80 g/l, acidifying the suspension with concentratedsulfuric acid to a pH below 7, thereafter separating the precipitatedsilica from the suspension by a filter press, washing, drying andmilling with a jet mill.
 5. The composition of claim 1, wherein saidprecipitated silica comprising about 15 to 20% by weight of thecomposition.
 6. The composition of claim 3, wherein said precipitatedsilica comprising about 15 to 20% by weight of the composition.
 7. Atransparent dental-care toothpaste composition having improved shelflife as set forth in claim 1 which additionally contains glycerol.
 8. Atransparent dental-care toothpaste composition having improved shelflife as set forth in claim 3 which additionally contains glycerol. 9.The transparent dental-care composition as set forth in claim 1 whichcontains at least one of the group consisting of a binder, apreservative, a sweetener, an aromatic oil, a foaming agent, a fluorideand a dye.
 10. The transparent dental-care composition as set forth inclaim 3 which contains at least one of the group consisting of a binder,a preservative, a sweetener, an aromatic oil, a foaming agent, afluoride and a dye.
 11. A transparent dental-care toothpaste compositionaccording to claim 1 which additionally comprises blue dye solution,carboxymethylcellulose, sodium salt of methyl p-hydroxybenzoate,saccharin, glycerol, polyethyleneglycol, an aromatic oil and sodiumlauryl sulfate.
 12. A transparent dental-care toothpaste compositionaccording to claim 3 which additionally comprises blue dye solution,carboxymethylcellulose, sodium salt of methyl p-hydroxybenzoate,saccharin, glycerol, polyethyleneglycol, an aromatic oil and sodiumlauryl sulfate.
 13. A transparent dental-care toothpaste composition forsmokers according to claim 3 wherein the precipitated silica abrasiveagent has the following characteristics:

    ______________________________________                                        BET surface area determined                                                                      m.sup.2 /g                                                                            15-110                                             according to DIN 66,131                                                       Tamped density     g/l     90-650                                             Secondary particle size                                                                          according to FIG. 2                                        distribution curve according                                                  to Coulter counter                                                            "ALPINE" screen retainings                                                                       % by    <0.1                                               >63 μm          weight                                                     Cu abrasion in 10% strength                                                                      mg      16-18                                              glycerol dispersion                                                           Viscosity of a 30% strength                                                                      mPa · s                                                                      30,000-60,000.                                     dispersion in a 1:1 water/                                                    glycerol mixture (Brookfield                                                  RTV Sp 5)                                                                     ______________________________________                                    


14. A transparent dental-care toothpaste composition as set forth inclaim 1, wherein the abrasive silica has a BET surface area 103 m² /gand an ALPINE screen retainings of 1.4% by weight, a Cu abrasion of 14,a viscosity of 36,000, and a lightness value of 94.4, wherein theviscosity is determined in 15% strength dispersion in a 1:1glycerol/water mixture.
 15. A transparent dental-care toothpastecomposition according to claim 1, wherein the silica has a BET surfacearea of 70 m² /g, an ALPINE screen retainings of 0.1% by weight, a Cuabrasion of 12, a viscosity of 38,400 and a lightness value of 95.7. 16.A transparent dental-care toothpaste composition according to claim 1,wherein the silica has a BET surface area of 101 m² /g, an ALPINE screenretainings of 0.1% by weight, a Cu abrasion of 8 and a lightness valueof 96.8.
 17. The dental-care composition according to claim 1, whereinthe abrasive silica has a BET surface area of 51 m² /g, an ALPINE screenretainings of 0.1% by weight, a Cu abrasion of 17, a viscosity of 33,500and a lightness value of 94.6.
 18. The transparent dental-caretoothpaste composition according to claim 1 which additionally comprisespolyethyleneglycol
 400. 19. The transparent dental-care toothpastecomposition according to claim 1 which additionally comprisespolythyleneglycol 1500.